1. Field of the Invention
The present invention relates to a dielectric ceramic composition having reduction resistance and a method of production of the same and a multilayer ceramic capacitor or other electronic device using this dielectric ceramic composition.
2. Description of the Related Art
Electronic devices such as a multilayer ceramic capacitor are widely being utilized as small sized, large capacity, high reliability electronic devices. A large number is used in each piece of electronic apparatus. In recent years, along with the increasingly smaller sizes ad higher performances of such apparatus, greater demands have been made for further reduction in size, increase in capacity, reduction in price, and improvement of reliability of a multilayer ceramic capacitor.
A multilayer ceramic capacitor is usually produced by successively laminating an internal electrode layer paste and dielectric layer paste by the sheet method, printing method, etc. and simultaneously firing the internal electrode layers and dielectric layers in the stack.
As the conductive material of the internal electrode layers, generally Pd or a Pd alloy is used, but Pd is expensive, so relatively inexpensive Ni, Ni alloys, and other base metals have been coming into use. When using a base metal as the conductive material of the internal electrode layers, if firing in the air, the internal electrode layers are oxidized, so the dielectric layers and internal electrode layers have to be simultaneously fired in a reducing atmosphere. However, if firing in a reducing atmosphere, the dielectric layers are reduced and the specific resistance declines. For this reason, nonreducing dielectric materials have been developed.
However, a multilayer ceramic capacitor using a nonreducing dielectric material has the problem of remarkable degradation of the IR (insulation resistance) due to application of an electrical field, a short IR lifetime, and a low reliability.
Further, a capacitor is required to exhibit good capacity-temperature characteristics. In particular, depending on the application, it is required to exhibit flat capacity-temperature characteristics under severe conditions. In recent years, multilayer ceramic capacitors have come into use for engine electronic control units (ECU) mounted in engine compartments of automobiles, crank angle sensors, antilock brake system (ABS) modules, and other various types of electronic apparatuses. These electronic apparatuses are used for stable engine control, drive control, and brake control and are required to exhibit good circuit temperature stability.
The environment in which these electronic apparatuses are used falls in temperature to below −20° C. in the winter in cold locations. Further, after engine startup, in the summer, the temperature is projected as rising to as high as +130° C. or more. Recently, the wire harnesses used for connecting these electronic apparatuses with their controlled equipment have been eliminated and electronic apparatuses have even begun to be mounted outside the automobiles. Therefore, the environment to which these electronic apparatuses are exposed has been getting more severe. Accordingly, the capacitors used in these electronic apparatuses are required to exhibit flat temperature characteristics in a broad temperature range. Specifically, it is not sufficient when the capacitor-temperature characteristics only satisfy the X7R characteristic of EIA standard (−55 to 125° C. and ΔC/C=within ±15%), and a dielectric ceramic composition satisfying the X8R characteristics of EIA standard (−55 to 150° C. and ΔC/C=within ±15%) is required.
In this regard, the assignee has already proposed a dielectric ceramic composition able to be fired in a reducing atmosphere, having a high permittivity, and satisfying the X8R characteristics in the following explained Japanese Patent No. 3348081 and Japanese Patent No. 3341003.
However, in Japanese Patent No. 3348081 and Japanese Patent No. 3341003, there was the problem that if improving the high temperature accelerated lifetime by raising the annealing temperature after firing, the capacity defect rate of the products (ratio of products where capacity ends up falling below specified value) ended up becoming higher. For this reason, keeping down the capacity defect rate and improving the high temperature accelerated lifetime remains a challenge.